PRIOR CONCURRENT THERAPY: Biologic therapy: At least 7 days since prior anti-thymocyte globulin Chemotherapy: Concurrent cyclosporine, methotrexate, tacrolimus, mycophenolate mofetil, or prednisone allowed if plan in place to taper or discontinue Endocrine therapy: See Disease Characteristics Radiotherapy: Not specified Surgery: Not specified Other: At least 7 days since prior investigational agents At least 7 days since prior immunosuppressive agents At least 24 hours since prior drugs that suppress gastric acid secretion (e.g., H2 receptor antagonists or omeprazole) No concurrent drugs that suppress gastric acid secretion